Peptide-based PET/CT imaging visualizes PD-L1-driven radioresistance in glioblastoma

Radioresistance remains a great challenge for radiotherapy in the treatment of glioblastoma (GBM). PD-L1 expression is a key contributor to radioresistance and immune escape in GBM. The lack of effective methods to monitor the change of PD-L1 during radiotherapy in patients limits timely intervention and management of the resistance. Here, we developed a novel peptide tracer [18F]AlF-NOTA-PCP2 for PET/CT to visualize the changes of PD-L1 expression in response to radiotherapy, revealing PD-L1-driven radioresistance in GBM. The [18F]AlF-NOTA-PCP2 demonstrated high specificity and binding affinity to PD-L1 in vitro. The uptake of [18F]AlF-NOTA-PCP2 on PET/CT showed a strong positive correlation with PD-L1 expression by immunohistochemistry (IHC) (R² = 0.861, P < 0.001) in GBM xenograft tumors. The radiotracer uptake in PD-L1-positive tumors significantly increased post-radiotherapy (21.25 ± 0.91 % vs. 25.12 ± 0.82 %, P = 0.008), aligning with the radioresistance observed in these tumors. In vitro studies revealed that PD-L1-driven radioresistance by enhancing DNA damage repair through upregulation of RAD51 after activation of the PI3K-Akt pathway in cells. Preliminary clinical application in a radiotherapy-treated GBM patient demonstrated the ability to monitor PD-L1 dynamics, supporting its potential for clinical translation. Collectively, this peptide-based small molecule PET/CT radiotracers offer a noninvasive, real-time, and quantitative method to dynamically visualize PD-L1-driven radioresistance in GBM. It could serve as a potential radiotracer for facilitating patient stratification, adjusting radiotherapy regimens, and guiding personalized immunotherapy strategies.